1. Field of the Disclosure
The present disclosure relates to a synchronization detecting circuit that detects a voltage amplitude of a single-phase AC voltage source as a synchronization target and a frequency difference and a phase difference between the single-phase AC voltage source and a voltage source on the synchronization detecting circuit side. In addition, the present disclosure relates to an automatic synchronous parallelization apparatus that adjusts a voltage amplitude, a frequency, and a phase of a single-phase voltage-type DC-to-AC converting device performing an autonomous parallel operation.
2. Discussion of the Background Art
In order to synchronize two single-phase AC voltage sources, the voltage amplitude of a single-phase AC voltage source as a synchronization target and the frequency difference and the phase difference between the two single-phase AC voltage sources need to be detected. A technology, which is shown in FIG. 4, for detecting these is known.
According this technology, for each signal-phase AC voltage source, a voltage is sampled for each predetermined period, and a change amount per one sample (corresponding to a differential value) and a change in the change amount (corresponding to a second-order differential) per one sample are calculated. Then, based on the derived values, the voltage amplitude, the frequency, and the phase are acquired, and then, differences thereof are calculated (for example, see Japanese Patent Application Laid-Open (JP-A) No. 52-40174).
In addition, a technology for suppressing an inrush current at the time of connecting an inverter in parallel with a power system is known (for example, see JP-A No. 09-028040). In JP-A No. 09-028040, a technology is disclosed in which a filter capacitor of an inverter is charged with a current having a phase led by 90 degrees from a voltage of the power system, and the inverter is connected in parallel with the power system after the voltage of the filter capacitor becomes the same as that of the power system.
Furthermore, a single-phase voltage-type DC-to-AC converting device that performs an autonomous parallel operation by being connected in parallel with a single-phase voltage source such as a power system or a generator is known (for example, see JP-A No. 2009-219263). In JP-A No. 2009-219263, a single-phase voltage-type DC-to-AC converting device that is operated by being coupled with an external single-phase AC voltage source by generating a single-phase AC voltage having a predetermined phase difference from the phase of the external single-phase AC voltage source and adjusting the amplitude, the frequency, and the phase of the generated single-phase AC voltage is disclosed.
According to the technology disclosed in JP-A No. 52-40174, a sample voltage value is differentiated, and accordingly, there is a problem in that the influence of harmonic components included in a voltage waveform may be significant. Furthermore, division is used with an AC value being used as a denominator for detection of the frequency, and accordingly, there is a problem of instability in a case where a “division by zero” occurs.
Thus, in order to solve the above-described problem, according to an aspect of the present disclosure, there is provided a synchronization detecting circuit that is not easily influenced by harmonic components and can reliably maintain stability.
A single-phase voltage-type DC-to-AC converting device performing an autonomous parallel operation is controlled to be a voltage source when viewed from the side of the single-phase voltage source such as a power system or a generator. In a case where a single-phase voltage-type DC-to-AC converting device performing an autonomous parallel operation is connected in parallel with the external single-phase AC voltage source, in order to suppress an inrush current, the output of the single-phase voltage-type DC-to-AC converting device needs to follow the frequency and the voltage amplitude of the single-phase voltage source that consistently change. However, according to the technology of JP-A No. 52-40174, the inverter is controlled to be a current source, and accordingly, the technology cannot be applied to a single-phase voltage-type DC-to-AC converting device that is controlled to be a voltage source. As above, there is a problem in that there is no technology for automatic synchronous parallelization performed by suppressing an inrush current by allowing the output of the single-phase voltage-type DC-to-AC converting device performing an autonomous parallel operation to follow the frequency and the voltage amplitude of the single-phase voltage source that consistently change.
In order to solve the above-described problem, according to another aspect of the present disclosure, there is provided an automatic synchronous parallelization device capable of suppressing an inrush current by automatically adjusting the magnitude, the frequency, and the phase of the voltage when a single-phase voltage-type DC-to-AC converting device performing an autonomous parallel operation is connected in parallel with an external single-phase AC voltage source.